GPRESOURCES-214 - wrong redirection for resources with absolute link URL (baseUrl mapper, filter)

Fixes the problem described in [GPRESOURCES-214](http://jira.grails.org/browse/GPRESOURCES-214) by checking the linkUrl value at the redirection. If the linkUrl is an absolute URL that URL will be used for the redirection directly, otherwise the redirection target will be constructed by using the context path, the static URL prefix and the linkUrl value.

At pull request #45, there was a short discussion about a failing test, which was related to the aforementioned issue. The test itself was introduced with commit 36a857e8 and reverted at commit 98ac01d.

Besides a new unit test for the ResourceProcessor, I also reverted / re-added the LegacyResourceIntegrationSpec from commit 36a857e8 and fixed it (test mapper was not taken into account, yet). All of the tests are green.